JP5355327B2 - Ultrasonic diagnostic equipment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce unnecessary components in an integration of two-dimensional spectrum data. <P>SOLUTION: A 2D FFT process section 20 executes a frequency analysis of reception signals, which are repeatedly acquired from the interior of a range gate defining the depth range in a subject, in each of the depth direction and the repetition direction to acquire a two-dimensional power spectrum of Doppler frequency. An integration process section 22 integrates the two-dimensional power spectrum data along a straight line corresponding to a constant speed to acquire integration data on the speed. In this case, the integration process section 22 integrates within a limited integration range so as to reduce the unnecessary components in the integration. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to an ultrasonic diagnostic apparatus, and more particularly to a technique for obtaining Doppler information based on two-dimensional spectrum data.

  A technique of pulse Doppler (PW Doppler) that obtains Doppler information based on a received signal that is repeatedly obtained from within a range gate in which a range in the depth direction is determined by repeatedly transmitting ultrasonic pulse waves is known. Further, in this pulse Doppler, a technique for obtaining two-dimensional spectrum data of a Doppler frequency by performing frequency analysis on each of a depth direction and a repetition direction of a received signal obtained repeatedly is known (for example, Patent Documents). 1).

  When the two-dimensional spectrum data of the Doppler frequency is used, the two-dimensional spectrum data is integrated along the integration direction corresponding to a certain speed, and thereby the integrated data of the spectrum related to the speed (for example, the integrated power value). ) Can be obtained.

JP-A-2-68045

  However, in the technique using the above-described two-dimensional spectrum data, when integrating along the integration direction corresponding to a constant speed, if all of the spectrum data along the integration direction is integrated, for example, Even unwanted components (side lobes) generated in the frequency analysis and clutter components obtained from the clutter, such as clutter components that are undesirable in terms of integration, are accumulated.

  Under such circumstances, the inventors of the present application have conducted research and development on a technique using two-dimensional spectrum data.

  The present invention has been made in the course of research and development, and its object is to reduce unnecessary components in the integration of two-dimensional spectral data.

  A suitable ultrasonic diagnostic apparatus for the above purpose includes a probe for transmitting / receiving ultrasonic waves to / from a subject, a transmission / reception unit for obtaining a received signal from within the subject by controlling the probe, and a depth measurement in the subject. A frequency analysis unit that obtains two-dimensional spectrum data of a Doppler frequency by performing frequency analysis on each of a depth direction and a repetition direction for a received signal that is repeatedly obtained from within a range gate that defines a range, and the two-dimensional The spectral data is integrated within a limited integration region along an integration direction corresponding to a constant speed, and an integration unit for acquiring the integration data of the speed is formed, and a Doppler image is formed based on the integration data. And a Doppler image forming unit.

  In a preferred embodiment, the integration region is a region in which a range in the depth direction of two-dimensional spectrum data is limited according to a transmission frequency band.

  In a preferred embodiment, the integration region is a region obtained by removing a low frequency band corresponding to clutter in a two-dimensional spectrum data repetition direction.

  In a preferred embodiment, the integration region is a region that is line-symmetric with respect to a straight line corresponding to the transmission center frequency.

  In a preferred specific example, the integration region is a region having a boundary in an integration direction corresponding to a predetermined speed.

  Preferably, the integration is performed after weighting processing is performed on the integration target data in the vicinity of the boundary.

  According to the present invention, unnecessary components are reduced in integrating two-dimensional spectrum data.

1 is a diagram showing an overall configuration of a preferable ultrasonic diagnostic apparatus of the present invention. It is a figure for demonstrating a two-dimensional FFT process. It is a figure for demonstrating the unnecessary component in integration. It is a figure which shows the limited integration area | region in integration. It is a figure for demonstrating the return of the straight line in integration. It is a figure which shows the integration result accompanying having limited the integration area | region.

  Hereinafter, preferred embodiments of the present invention will be described.

  FIG. 1 is a diagram showing an overall configuration of an ultrasonic diagnostic apparatus suitable for implementing the present invention. The probe 10 is an ultrasonic probe that transmits and receives ultrasonic waves to a subject such as a living body. The probe 10 includes a plurality of vibration elements each of which transmits and receives an ultrasonic wave. The plurality of vibration elements are transmission-controlled by the transmission beam former 12 to form a transmission beam. In addition, the plurality of vibration elements receive the ultrasonic waves reflected from the subject, and signals obtained thereby are output to the reception beam former 14, and the reception beam former 14 forms a reception signal along the reception beam. .

  The gate processing unit 16 sets a range gate that defines a range of depth within the subject. For example, when the user designates a desired position in the living body using an operation device while viewing a B-mode image or the like, the range gate is set at the designated position. The range (width) of the range gate may be set by the user.

  The ultrasonic diagnostic apparatus in FIG. 1 repeatedly transmits and receives ultrasonic waves in the same beam direction, and obtains Doppler information from a moving body such as a blood flow, for example, based on reception signals obtained repeatedly from within the range gate. At that time, the 2D FFT processing unit 20 performs a two-dimensional FFT process on the repeatedly obtained reception signal stored in the memory or the like. Thereby, two-dimensional spectrum data is obtained. The two-dimensional FFT process will be described in detail later.

  The integration processing unit 22 integrates the two-dimensional spectrum data in an integration region limited along the integration direction corresponding to a constant speed, thereby obtaining integrated data corresponding to the constant speed. The integration in the integration processing unit 22 will be described in detail later.

  The image forming unit 24 forms a display image such as a Doppler waveform indicating a time change of the Doppler signal based on the accumulated data corresponding to each speed obtained by the accumulation processing unit 22. Each unit in the ultrasonic diagnostic apparatus in FIG. 1 is controlled by the control unit 30.

  FIG. 2 is a diagram for explaining the two-dimensional FFT processing. FIG. 2A shows a received signal obtained repeatedly from within the range gate. A large number of circles shown in FIG. 2A are sampled received signal data, and the received signal data is shown two-dimensionally by setting the horizontal axis as the depth direction and the vertical axis as the repeat direction. Yes. The reception signal data is, for example, the amplitude value of the reception RF signal. In addition, as the received signal data, for example, the amplitude value of the in-phase component (I signal) and the amplitude value of the quadrature component (Q signal) regarding the baseband signal after quadrature detection may be used. The two-dimensional received signal in FIG. 2A is stored in, for example, a memory or the like, and the 2D FFT processing unit 20 (FIG. 1) uses the two-dimensional received signal data stored in the memory or the like. Perform dimension FFT processing.

  In the two-dimensional FFT processing, frequency analysis is performed in each direction of the depth direction and the repetition direction. For example, the received signal is subjected to frequency analysis in the depth direction, and an amplitude value (complex amplitude value) for each frequency component is calculated. The frequency analysis regarding the depth direction is executed for each of a plurality of received signals arranged in the repetition direction. Then, when the analysis in the depth direction regarding the plurality of received signals is completed, the frequency analysis regarding the repetition direction is executed for the amplitude value (complex amplitude value) for each frequency component obtained by the analysis. The frequency analysis regarding the repetition direction is executed for each of a plurality of frequency components obtained by the analysis in the depth direction.

  FIG. 2B shows a two-dimensional power spectrum obtained as a result of the two-dimensional FFT process. The horizontal axis in FIG. 2B indicates the frequency in the depth direction. The spectrum in the depth direction of the received signal agrees with the spectrum of the transmitted signal when neglecting the influence of minute Doppler shift and attenuation and scattering caused by tissue. Therefore, the horizontal axis in FIG. 2B corresponds to a plurality of frequencies included in the transmission signal.

Moreover, the power (or amplitude value) for each Doppler frequency is calculated by frequency analysis regarding the repetition direction. Since the frequency analysis for the repetition direction is performed for each frequency on the horizontal axis, the power of the Doppler frequency (Doppler shift frequency) corresponding to that frequency for each frequency on the horizontal axis, that is, for each frequency included in the transmission signal. Is calculated. For example, in FIG. 2B, the Doppler frequency obtained from the moving body at the speed v by the transmission center frequency f ₀ is f _d0 , and the power (or amplitude value) of the Doppler frequency f _d0 is f ₀ and f _d0. It is expressed by the luminance value, hue, etc. at the coordinate position determined by.

Incidentally, in the one-dimensional FFT processing that performs frequency analysis in the repetitive direction without performing frequency analysis in the depth direction, the Doppler frequency of the bandwidth R is measured by a transmission signal having a bandwidth at the transmission center frequency f _0. The On the other hand, as described above, the two-dimensional FFT process has an advantage that the Doppler frequency corresponding to the frequency can be identified for each frequency included in the transmission signal.

In the physical basic principle of Doppler shift, the Doppler frequency (Doppler shift frequency) relating to the moving body is proportional to the frequency of the ultrasonic wave used for measurement and the speed of the moving body. For example, when the velocity of the moving body along the ultrasonic beam direction is v and the frequency of the ultrasonic wave used for measurement (the frequency of the transmission signal) is f, the Doppler frequency f _d is f _d = (2v / C) · f (c is the speed of sound).

Therefore, in FIG. 2B, the correspondence between the transmission frequency f on the horizontal axis and the Doppler frequency f _{d on} the vertical axis for a moving body with a speed v is a straight line L passing through the origin and having an inclination of 2 v / c. . Therefore, when the power of the spectrum is integrated along the straight line L, an integrated power value related to the speed v can be obtained. In order to obtain the integrated power for each of the plurality of speeds v, the slope of the straight line L passing through the origin is changed according to the magnitude of the speed v, and along each of the plurality of straight lines L corresponding to the plurality of speeds v. What is necessary is just to calculate an integrated value.

  In the ultrasonic diagnostic apparatus of FIG. 1, the 2D FFT processing unit 20 executes a two-dimensional FFT process, and the integration processing unit 22 integrates the spectrum power along the straight line L. At that time, the integration processing unit 22 reduces unnecessary components in the integration by integrating within the limited integration region. Components unnecessary for integration include unnecessary components (side lobes) generated in frequency analysis, clutter components obtained from clutter, noise, and the like.

FIG. 3 is a diagram for explaining unnecessary components in the integration. In general, in FFT processing, a window function is used in order to prevent spectrum side lobes generated by FFT processing. FIG. 3I shows a two-dimensional power spectrum in the case where a window function is used in the FFT processing relating to the repetition direction on the vertical axis and no window function is used in the FFT processing relating to the depth direction on the horizontal axis. In FIG. 3, the luminance value (darkness of black) at each position determined by the coordinate value (frequency f) on the horizontal axis and the coordinate value (Doppler frequency f _d ) on the vertical axis is the power of the Doppler frequency corresponding to that position. Is shown. For example, relatively strong power is obtained in a frequency band corresponding to blood flow to be measured and a low frequency band corresponding to clutter.

  In FIG. 3I, since the window function is not used in the FFT processing related to the depth direction of the horizontal axis, side lobes are generated in the horizontal axis direction. That is, the power of the Doppler frequency is displayed even though it is outside the transmission frequency band. Incidentally, FIG. 3 (II) shows a two-dimensional power spectrum in which side lobes in the horizontal axis direction are reduced by using a window function in the FFT processing in the depth direction on the horizontal axis. From the comparison between FIGS. 3I and II, the side lobes in the horizontal axis direction in FIG. 3I can be understood. However, as shown in FIG. 3 (II), when a window function is used in the FFT processing in the depth direction of the horizontal axis, side lobes in the horizontal axis direction are reduced, but there is a possibility that degradation of resolution may be caused.

  Therefore, in the ultrasonic diagnostic apparatus of FIG. 1, the integration processing unit 22 integrates within a limited integration region, thereby reducing unnecessary components in the integration.

  FIG. 4 is a diagram showing a limited integration region in integration. FIG. 4 shows some specific examples relating to the integration region 50.

FIG. 4A shows an integration region 50 in which the range in the depth direction (horizontal axis) of the two-dimensional power spectrum is limited according to the transmission frequency band. The width of the integration area 50 in the horizontal axis direction is set to the same width as the transmission frequency band, for example. Further, when a two-dimensional power spectrum is obtained using a baseband signal after quadrature detection, the width of the integration region 50 in the horizontal axis direction is determined in consideration of the cutoff frequency of the low-pass filter in quadrature detection. . Furthermore, the integration region 50 has a line-symmetric region with respect to corresponding to the transmission center frequency f ₀ of the vertical axis line (not shown).

  For example, when integrating the power of the spectrum along the straight line L1 corresponding to the target speed, the integration processing unit 22 (FIG. 1) calculates the power of the spectrum outside the integration region 50 among the spectra on the straight line L1. Excluding from integration, integration is performed for only the power of the spectrum in the integration region 50. Thereby, the side lobes outside the transmission frequency band are excluded from the integration, and the influence of the side lobes on the integration result is reduced. Desirably, the effects of side lobes are completely eliminated.

  FIG. 4B shows the integration region 50 in which the low frequency band is removed in the repetition direction (vertical axis) in addition to the limitation of the range in the depth direction (horizontal axis) similar to FIG. 4A. . The low frequency band in the repetition direction is a region corresponding to clutter as shown in FIG. Therefore, by removing the low frequency band in the repetition direction as shown in FIG. 4B, the influence of clutter on the integration result can be reduced.

4C, like FIG. 4B, is an integration region 50 in which the low frequency band is removed in the repetition direction (vertical axis), and FIG. 4C shows a straight line corresponding to a predetermined speed. An integration region 50 having a boundary between L0 and a straight line L0 ′ is shown. The Doppler frequency f _d related to the clutter is also proportional to the transmission frequency f (f _d = (2v / c) · f). In the integration region 50 of FIG. 4C, a region excluded from integration according to this proportional relationship. Is set. In order to prevent the Doppler image from unnaturally changing at the boundary of the clutter portion, for example, the integration target data may be weighted in the vicinity of the straight line L0 and the straight line L0 ′ and then integrated.

  For example, by using the integration region 50 shown in FIG. 4, it is possible to exclude unnecessary components (side lobes) generated in frequency analysis, clutter components obtained from clutter, and the like from integration. In addition, as described above, a straight line corresponding to a constant speed is used in the integration. In Doppler shift, the Doppler frequency folding phenomenon is known. The Doppler shift is also taken into consideration for the straight line in the integration.

  FIG. 5 is a diagram for explaining the folding of a straight line in integration. FIG. 5 shows the same coordinate system as the two-dimensional power spectrum with the horizontal axis as the depth direction (transmission frequency) and the vertical axis as the repetition direction (Doppler frequency). On the coordinate system, a straight line L2 corresponding to a positive constant speed and a straight line L3 corresponding to a negative constant speed are shown.

  The straight line L2 starts from the origin O, increases in the vertical axis direction as the transmission frequency on the horizontal axis increases, and reaches the position of the Doppler frequency PRF / 2 on the vertical axis. PRF is a pulse repetition frequency, and a folding phenomenon occurs for a Doppler frequency exceeding PRF / 2. Therefore, the folding corresponding to the Doppler frequency is also considered for the straight line L2. That is, when the straight line L2 reaches the position of the Doppler frequency PRF / 2 on the vertical axis, the straight line L2 is folded back to the position of the Doppler frequency −PRF / 2 on the vertical axis while the position of the transmission frequency on the horizontal axis is fixed. From the position of the Doppler frequency −PRF / 2 on the vertical axis, the vertical axis increases as the transmission frequency on the horizontal axis increases while maintaining the inclination before folding.

  Similar to the straight line L2, the return of the straight line L3 is considered. That is, the straight line L3 starts from the origin O, decreases in the vertical axis direction as the transmission frequency on the horizontal axis increases, and reaches the position of the Doppler frequency −PRF / 2 on the vertical axis. When the straight line L3 reaches the position of the Doppler frequency −PRF / 2 on the vertical axis, the straight line L3 is folded back to the position of the Doppler frequency PRF / 2 on the vertical axis while fixing the position of the transmission frequency on the horizontal axis. Furthermore, from the position of the Doppler frequency PRF / 2 on the vertical axis, while maintaining the inclination before folding, the vertical axis decreases as the transmission frequency on the horizontal axis increases.

  In this way, the Doppler shift is also taken into consideration for the straight line for integration. Even in the case where the straight line is folded, only the area within the integration area is targeted for integration on the straight line.

  FIG. 6 is a diagram illustrating an integration result associated with limiting the integration region. The horizontal axis in FIG. 6 corresponds to the speed of the moving body, and the speed of the moving body is expressed by the Doppler frequency. The vertical axis in FIG. 6 shows the integrated value (integrated power) for each speed of the moving body.

  In FIG. 6, a waveform 62 represented by a broken line is obtained from a two-dimensional power spectrum (see FIG. 3I) in the case where the window function is not used and the integration region is not limited in the FFT processing in the depth direction. This is the integration result. On the other hand, the waveform 60 represented by a solid line does not use a window function in the FFT processing in the depth direction, and uses a two-dimensional power using an integration region (FIG. 4A) limited according to the transmission frequency band. It is the integration result obtained from the spectrum.

  Comparing the waveform 60 and the waveform 62, the waveform 62 shows a relatively large value in a portion other than the blood flow. This is mainly due to the influence of side lobes outside the transmission frequency band, and it can be confirmed that the influence is reduced in the waveform 60.

  Incidentally, the waveform 64 is an integration result obtained from a two-dimensional power spectrum (see FIG. 3 (II)) when the integration function is not limited using a window function in the FFT processing in the depth direction. Comparing the waveform 60 and the waveform 64, it can be confirmed that the side lobes in the waveform 60 are reduced to the same extent as the waveform 64, that is, to the same extent as when the window function is used in the FFT processing in the depth direction. As described above, in the case of the waveform 64 using the window function, although the side lobe is reduced, there is a possibility of degrading the resolution.

  Further, the waveform 60 is a result obtained by using the integration region limited according to the transmission frequency band, that is, the integration region 50 of FIG. 4A, and the clutter component is not a reduction target. For this reason, in the waveform 60 of FIG. However, the clutter component can be excluded from the integration by using the integration region 50 in FIGS. 4B and 4C instead of the integration region 50 in FIG. That is, the clutter portion in the waveform 60 of FIG. 6 can be reduced by using the integration region 50 of FIGS.

  As mentioned above, although preferred embodiment of this invention was described, embodiment mentioned above is only a mere illustration in all the points, and does not limit the scope of the present invention. The present invention includes various modifications without departing from the essence thereof.

  10 probe, 12 transmit beamformer, 14 receive beamformer, 16 gate processing unit, 202DFFT processing unit, 22 integration processing unit, 24 image forming unit.

Claims (6)

A probe for transmitting and receiving ultrasonic waves to the subject;
A transmission / reception unit that obtains a reception signal from within the subject by controlling the probe; and
Frequency for obtaining two-dimensional spectrum data of Doppler frequency by performing frequency analysis for each of the depth direction and the repeat direction for the received signal obtained repeatedly from within the range gate that defines the depth range in the subject. An analysis unit;
An integrating unit that obtains integrated data of the speed by integrating the two-dimensional spectrum data in an integrated region limited along an integrating direction corresponding to a constant speed;
A Doppler image forming unit that forms a Doppler image based on the accumulated data;
Having
An ultrasonic diagnostic apparatus. The ultrasonic diagnostic apparatus according to claim 1,
The integration region is a region in which a range in the depth direction of two-dimensional spectrum data is limited according to a transmission frequency band.
An ultrasonic diagnostic apparatus. The ultrasonic diagnostic apparatus according to claim 2,
The integration region is a region obtained by removing a low frequency band corresponding to clutter in the repeating direction of two-dimensional spectrum data.
An ultrasonic diagnostic apparatus. The ultrasonic diagnostic apparatus according to claim 2,
The integration region is a region that is line-symmetric with respect to a straight line corresponding to the transmission center frequency.
An ultrasonic diagnostic apparatus. The ultrasonic diagnostic apparatus according to claim 3.
The integration area is an area having a boundary in an integration direction corresponding to a predetermined speed.
An ultrasonic diagnostic apparatus. The ultrasonic diagnostic apparatus according to claim 5,
Accumulate after applying a weighting process to the integration target data in the vicinity of the boundary,
An ultrasonic diagnostic apparatus.

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